The present disclosure generally relates to corrosion, and, more specifically, to methods for suppressing corrosion of sensitive metal components during subterranean treatment operations.
Treatment fluids can be used in a variety of subterranean treatment operations. Such treatment operations can include, without limitation, drilling operations, stimulation operations, production operations, remediation operations, sand control treatments, and the like. As used herein, the terms “treat,” “treatment,” “treating,” and grammatical equivalents thereof refer to any subterranean operation that uses a fluid in conjunction with achieving a desired function and/or for a desired purpose. Use of these terms does not imply any particular action by the treatment fluid or a component thereof, unless otherwise specified herein. More specific examples of illustrative treatment operations can include, for example, drilling operations, fracturing operations, gravel packing operations, acidizing operations, scale dissolution and removal operations, sand control operations, consolidation operations, and the like.
Corrosive environments comprising an acid can cause severe corrosion damage to many types of metal surfaces. As used herein, the term “corrosion” and grammatical variants thereof will refer to any reaction between a metal surface and its surrounding environment that causes a deterioration or change in the metal surface's properties or morphology. Examples of corrosion damage to a metal surface include, but are not limited to, rusting, metal dissolution or erosion, pitting, peeling, blistering, patina formation, and any combination thereof.
Acidic treatment fluids are frequently utilized in the course of conducting various subterranean treatment operations. Illustrative uses of acidic treatment fluids during subterranean treatment operations include, for example, matrix acidizing of siliceous and/or non-siliceous formations, scale dissolution and removal operations, gel breaking, acid fracturing, and the like. When acidizing a non-siliceous material, such as a carbonate material, mineral acids such as hydrochloric acid may often be sufficient to affect dissolution. Organic acids may be used in a similar manner to hydrochloric acid when dissolving a non-siliceous material. Siliceous materials, in contrast, are only readily dissolvable using hydrofluoric acid, optionally in combination with other acids. Illustrative siliceous materials can include, for example, silica, silicates, aluminosilicates, and any combination thereof, optionally in further combination with a non-siliceous material, such as a carbonate material.
Corrosion of metal surfaces within a wellbore penetrating a subterranean formation, such as tubulars and tools, for example, can be highly undesirable due to the difficulty, cost, and production downtime associated with replacing such components. In many instances, elevated temperatures within subterranean formations can dramatically accelerate downhole corrosion rates.
Metal surfaces in fluid communication with a wellbore can similarly be susceptible to corrosion and its undesirable effects. In subsea wellbores, for example, a subsea riser structure extending from the wellbore to a platform or vessel on the ocean's surface or just below the ocean's surface can be susceptible to corrosion, in spite of the low temperatures of deep water environments. Outside the wellbore, corrosion can occur during introduction of a treatment fluid to the wellbore, during production, or any combination thereof. Regardless of its location, corrosion-induced damage of a metal surface can represent a significant safety and/or environmental concern due to potential well failure issues.
Although almost all acids represent a potential corrosion threat to many metal surfaces, hydrofluoric acid can be especially damaging when contacting certain types of sensitive metal surfaces. Illustrative examples of particularly sensitive metal surfaces include those containing titanium. Titanium and titanium alloys are lightweight, strong and resistant to most formation fluids and a great number of common treatment fluids, including those containing organic acids and/or mineral acids such as hydrochloric acid. However, titanium and titanium alloys are especially prone to corrosion by even modest quantities of hydrofluoric acid at pH values of about 7 or less. The extreme sensitivity of titanium and titanium alloys to hydrofluoric acid can preclude use of this metal in situations where acidizing of a siliceous material is anticipated to take place. For example, titanium and titanium alloys frequently form at least a portion of subsea riser structures for use in conveying fluids to and from a deepwater wellbore. Due to the propensity of titanium toward corrosion by hydrofluoric acid, it can be especially difficult to conduct stimulation operations in deepwater wellbores containing a siliceous material.
In some instances, corrosion inhibitors can be used to reduce the propensity of a metal surface to undergo corrosion-induced damage by acids. As used herein, the terms “inhibit,” “inhibitor,” “inhibition” and other grammatical forms thereof generally refer to the lessening of the tendency of a phenomenon to occur and/or the degree to which that phenomenon occurs. The terms “suppress,” “suppression” and other grammatical forms thereof may be used equivalently herein. The term “inhibit” and equivalents thereof do not imply any particular extent or amount of inhibition or suppression unless otherwise specified herein. Although the corrosiveness of hydrochloric acid and organic acids can usually be effectively suppressed using a variety of common corrosion inhibitors, conventionally used corrosion inhibitors are often much less effective for inhibiting the corrosiveness of hydrofluoric acid, particularly for titanium and titanium alloy surfaces. Without being bound by theory or mechanism, it is believed that a passivating layer of TiO2 on titanium metal surfaces is readily removed by hydrofluoric acid, thereby making the underlying titanium metal or titanium alloy extremely susceptible to further corrosion upon its removal. Although inhibited titanium alloys (e.g., Ti Grade 29 alloy, which is inhibited by small amounts of ruthenium, or Ti Grade 7 alloy, which is inhibited by small amounts of palladium) can display a decreased propensity toward corrosion in the presence of hydrofluoric acid than do pristine titanium or uninhibited alloys (e.g., commercially pure Ti, CP—Ti), corrosion is often still an issue. Moreover, cost and sourcing of inhibited titanium alloys can be problematic, especially for large-scale operations.